Preacher no longer one who thumps (9)
I believe the answer is:
expounder
'preacher' is the definition.
(thesaurus)
'no longer one who thumps' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'one who thumps' becomes 'pounder' (someone who pounds or thumps).
'ex'+'pounder'='EXPOUNDER'
(Other definitions for expounder that I've seen before include "interpreter" , "One fully describes" .)